Research Document - 2012/152

Reference points and assessment update for American Plaice (Hippoglossoides platessoides) in NAFO SA2 + Div. 3K and Subdiv. 3Ps

By M.J. Morgan, K.S. Dwyer, and P.A. Shelton

Abstract

Survey indices from research vessel (RV) and landings information were updated for Subarea (SA) 2 + Div. 3K and Subdiv. 3Ps American Plaice (Hippoglossoides platessoides).  Limit reference points (LRP) were determined for these two stocks and stock status updated relative to these points.

In SA2 + Div. 3K the stock declined to very low levels by the early 1990s.  Total mortality due to all causes, including fishing, has been decreasing on more recent cohorts but, stock biomass remains at only 10% of the values of the mid-1980s.  An empirical biological LRP was determined from examining stock recruit data from the research vessel survey.  Generally recruitment has been impaired when the survey spawning stock biomass (SSB) index is below 70,000 t and therefore this was chosen as the LRP.  The 2009 estimate of survey spawning stock biomass (SSB; the most recent year for which age data are available) indicates that the stock is at 24% of the LRP.  It was not possible to determine an upper reference point or a removals (F-based) reference point for this stock.

In Subdiv. 3Ps a Bayesian Surplus Production Model was applied to landings data from 1960 to 2010 and survey data from 1980 to 2010.  Consistent with the Fisheries and Oceans Canada (DFO) Precautionary Approach (PA) policy B_lim is 40% B_msy, the upper stock reference is 80% B_msy and F_lim is F_msy.  Stock status relative to these reference points was estimated from the model.  Stock size estimated from the surplus production model decreased fairly steadily from the late 1960s to reach a low in 1993 of less than 10% of B_msy.  Stock size has been increasing slowly since 1993; however, current biomass is 50% of B_lim and therefore the stock is in the critical zone.  The probability of being below B_lim is high (0.94).  Current fishing mortality is estimated to be 64% of F_lim.  The probability of being above F_lim is 0.2.

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